1. Field of the Invention
The present invention relates to a lens unit including a plurality of transparent resin lenses and a manufacturing method thereof. More concretely, the invention relates to the lens unit where a plurality of resin lenses are held in a lens barrel which covers them, and the manufacturing method thereof.
2. Description of the Related Art
Conventionally, a lot of transparent lenses made of resin are used as optical lenses. Particularly a plurality of resin lenses are mostly combined to be used as lenses for cameras. For this reason, the resin lenses or the resin lenses and a lens barrel for holding them should be fixed to one another. In such resin lenses, an area for joining is formed integrally with outer peripheries of effective areas of the lenses, and these areas are joined by utilizing adhesive or ultrasonic welder.
On the contrary, U.S. Pat. No. 4,636,609 and Japanese Patent Application Laid-Open No. 2003-181931 disclose a method of joining resin materials using laser beam. For example, U.S. Pat. No. 4,636,609 discloses the joining method of superposing an absorptive material and an unabsorbable material with respect to laser beams and emitting a laser beam to a side of the unabsorbable material. Further, Japanese Patent Application Laid-Open No. 2003-181931 discloses the joining method of holding a thin infrared absorptive transparent film between transparent resin members and emitting a laser beam thereto. Japanese Patent Application Laid-Open No. 7-92301 discloses a resin lens in which ultraviolet absorbent or infrared absorbent is mixed in a transparent lens so that transmittance for each wavelength region is adjusted.
The conventional joining method for the lens units, however, has the following problems. In the joining method using adhesive, it takes a long time to apply and harden adhesive. Further, an appearance problem due to wrap-around of the adhesive to the lens surface or the like possibly arises. In the joining method using the ultrasonic welder, since a horn should be used for pushing, a shape and a size of the lens are limited. Further, in a miniature lens unit or the like which is used in miniature cameras of cellular phones or the like, a work for holding an infrared absorptive film is not easy, and a number of parts increases, thereby possibly deteriorating assembly workability.